Recently, novel lubricant compositions (referred to in this specification as HVI-PAO) produced by oligomerising alpha-olefins and having high values of viscosity index have been disclosed in U.S. Pat. Nos. 4,827 and 4,827,073, to which reference is made for a description of these compositions and of their preparation. These materials are produced by oligomerising the alpha-olefin starting material in the presence of an oligomerisation catalyst comprising reduced chromium on a silica support specifically, the oligomers are produced by contacting a C.sub.6 -C.sub.20 1-alkene feedstock with reduced valence state chromium oxide catalyst on porous silica support under oligomerizing conditions in an oligomerization zone to produce the desired high viscosity, high viscosity index (VI) liquid hydrocarbon lubricant. These oligomers are distiguished by having branch ratios less than 0.19 and the lubricants have notably low pour points, e.g. pour points below -15.degree. C. Lubricants produced by the process cover the full range of lubricant viscosities and exhibit a remarkably high VI and low pour point even at high viscosity. The as-synthesized HVI-PAO oligomer has olefinic unsaturation associated with the last of the recurring monomer units in the structure.
Notwithstanding their generally superior properties, HVI-PAO lubricants are often formulated with additives to enhance those properties for specific applications. The additives which are more commonly used in lubricants include oxidation inhibitors, rust inhibitors, metal passivators, antiwear agents, extreme pressure additives, pour point depressants, detergent-dispersants, viscosity index improvers, foam inhibitors and the like. This aspect of the lubricant arts is specifically described in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd edition, Vol. 14, pp.477-526, to which reference is made for a description of such additives. Improvements in lubricant technology have come both from new additive development addressed to deficiencies in lubricant basestocks and new basestocks for inherently better properties.
The inclusion of aromatic compounds in the lubricant mixture is known to improve thermal stability. Alkylated aromatics, particularly alkylated naphthalene, are known in the prior art as lubricant additives for their antiwear properties, thermal and oxidative stability as disclosed in U.S. Pat. Nos. 4,211,665, 4,238,343, 4,604,491 and 4,714,7944. Antiwear properties of alkylnaphthalene lubricating fluids are presented in Khimiya i Tekhnologiya Topliv i Masel, No. 8, pp. 28-29, August, 1986 and show promise as base stocks for lubricants.
A recurring problem in formulating a new lubricant with an additive package is the compatibility or solubity of the additive package in the lube, for specific components of the package may have only very limited solubility in the aliphatic hydrocarbon lubricant oligomer. This can necessitate the addition of further additives as solubilizing agents for the package, adding to the cost and complexity of the lube blend. Consequently, when the basic structure or backbone of the oligomer can be modified to include functional groups which confer desirable characteristics on the oligomer itself, for example, improved thermal stability or solubilizing characteristics, the foregoing lubricant formulation problems are mitigated.